The manufacturing of fiber-reinforced composite articles may include laying up composite plies over a forming tool to form a composite layup. Heat and pressure may be applied to the composite layup to consolidate and cure the composite layup into a cured composite article. Conventional methods of curing a composite layup may involve the use of an autoclave to provide heat and compaction pressure to the composite layup to achieve the desired mechanical properties in the cured composite article. The application of compaction pressure may facilitate the evacuation of entrapped moisture, air, and/or volatiles from the composite layup during consolidation and curing such that low porosity and high strength may be achieved in the cured composite article.
Unfortunately, the use of an autoclave for manufacturing a composite article may require extended periods of time to heat the composite layup to the required consolidation and curing temperatures and extended periods of time to cool the composite layup to ambient temperature after curing. The amount of time required to process and cure a composite layup in an autoclave may be prohibitive for large-scale production programs requiring high part-production rates. In addition, autoclaves are generally expensive to construct and operate. Furthermore, the internal size of an autoclave may represent an upper limit on the size of a composite layup that can be processed. A further drawback associated with autoclaves is that a portion of the moisture, air, and/or volatiles may remain inside the composite layup after curing.
Double-vacuum-bag processing allows for consolidation and curing of a composite layup without the need for an autoclave. In some examples, a double-vacuum-bag system may include inner and outer vacuum bags applied over a composite layup and sealed to a layup mandrel, cure tool, or forming tool. An outer shroud may be used to replace the outer vacuum bag for enclosing the inner vacuum bag with both the shroud and the inner bag being sealed to the forming tool. The double-vacuum-bag assembly may be installed in an oven for heating the composite layup. Because double-vacuum-bag processing uses only vacuum pressure to consolidate and remove moisture, air, and/or volatiles from a composite layup, the compaction pressure on the composite layup may be less than the compaction pressure available in an autoclave. The dependency on vacuum pressure to consolidate the composite layup means that an effective inner bag chamber seal is required between the vacuum bag and the forming tool to ensure the quality of the cured composite article. Any leakage in the inner bag chamber seal between the inner and outer vacuum bags and the forming tool during consolidation and/or curing may reduce the amount of compaction pressure that can be applied to the composite layup during cure. In addition, leakage in the inner bag chamber seal may introduce air and porosity into the composite layup during curing.
As can be seen, there exists a need in the art for a method of ensuring the integrity and effectiveness of an inner bag chamber seal during curing of a composite layup in a double-vacuum-bag curing process.